A variety of guides employed to properly position a medical instrument within the skull of a patient are known in the prior art, as evidenced by the devices disclosed in the following U.S. Pat. Nos. 3,016,899--Stenvall, 3,017,887--Heyer, 3,021,842--Flood, 3,055,370--McKinney et al., 3,115,140--Volkman, 3,135,263--Connelley, Jr.
As is shown in the above identified McKinney et al. U.S. Pat. No. 3,055,370 a guide for a surgical instrument intended to be used in the treatment of the brain includes a cranial tap which is adapted to be threaded into the skull of a patient, a spherical member rotatable within the tap and adapted to receive the surgical instrument therein, and a locking cap threadedly received within the upper end of the tap to immobilize the spherical member. This arrangement positions the surgical instrument in a proper orientation for performing a desired medical procedure, such as rendering a portion of the brain ineffective by electrical stimulation to treat people afflicted with Parkinson's diease.
Although a guide of the type disclosed in the McKinney et al. patent has been employed with success, Applicant, who is a neurosurgeon, is of the opinion that a new and improved guide is desired which is simpler in design and yet reliable in use to properly position and retain a surgical instrument for use in performing a medical procedure, particularly within the brain.